Zoom lens and image pickup apparatus including the same

Abstract

A zoom lens including a plurality of lens units, and two variable stops having an aperture diameter changing for zooming, the lens units being configured to change intervals between the respective neighboring lens units for zooming, the zoom lens having an F-number which is constant over an entire zoom range, the two variable stops including a first variable stop disposed on an object side, and a second variable stop disposed on an image side. A distance (Sw1) from the first variable stop to an image plane at a wide-angle end, a distance (Sw2) from the second variable stop to the image plane at the wide-angle end, and a distance (Tkw) from an exit pupil position to the image plane at the wide-angle end are each set appropriately.

What is claimed is:  
     
       1. A zoom lens, comprising, in order from an object side to an image side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power, the lens units being configured to change intervals between the respective neighboring lens units for zooming, the zoom lens having an F-number which is constant over an entire zoom range,
 the zoom lens comprising a first variable stop and a second variable stop, the first variable stop being disposed between the first lens unit and the second lens unit and having an aperture diameter changing for zooming, the second variable stop being disposed in an image side of the first variable stop and having an aperture diameter changing for zooming, 
 wherein the following conditional expressions are satisfied:
   0.90< Sw 1/ Tkw< 1.50, and 
   0.60< Sw 2/ Tkw< 1.00, 
 
 
       where Sw1 represents a distance from the first variable stop to an image plane at a wide-angle end, Sw2 represents a distance from the second variable stop to the image plane at the wide-angle end, and Tkw represents a distance from an exit pupil position to the image plane at the wide-angle end. 
     
     
       2. A zoom lens according to  claim 1 , wherein the following conditional expression is satisfied:
   0.8< Rwm /( Rwe ) 0.5 <1.5, 
 where Rwm represents a peripheral light intensity ratio at a 50 percent image height at the wide-angle end, and Rwe represents a peripheral light intensity ratio at a maximum image height at the wide-angle end. 
 
     
     
       3. A zoom lens according to  claim 1 , wherein at least one of lens surfaces adjacent to the first variable stop in an optical axis direction is a convex surface facing the first variable stop. 
     
     
       4. A zoom lens according to  claim 1 , wherein at least one of lens surfaces adjacent to the second variable stop in an optical axis direction is a convex surface facing the second variable stop. 
     
     
       5. A zoom lens according to  claim 1 , wherein the following conditional expression is satisfied:
   0.15< Es 1 t/En< 0.80, 
 
       where En represents a maximum effective diameter among effective diameters of lenses constructing the zoom lens, and Es1t represents an effective diameter of the first variable stop at a telephoto end. 
     
     
       6. A zoom lens according to  claim 1 , wherein the following conditional expression is satisfied:
   0.15< Es 2 t/En< 0.80, 
 
       where En represents a maximum effective diameter among effective diameters of lenses constructing the zoom lens, and Es2t represents an effective diameter of the second variable stop at a telephoto end. 
     
     
       7. A zoom lens according to  claim 1 , wherein:
 a sign of a combined focal length fA of all lens units disposed on the object side of the first variable stop is invariable over the entire zoom range; 
 a sign of a combined focal length fB of all lens units disposed between the first variable stop and the second variable stop is invariable over the entire zoom range; and 
 the sign of the combined focal length fA is opposite to the sign of the combined focal length fB. 
 
     
     
       8. A zoom lens comprising: in order from an object side to an image side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, a fourth lens unit having a positive refractive power, a fifth lens unit having a negative refractive power, and a sixth lens unit having a positive refractive power, the lens units being configured to change intervals between the respective neighboring lens units for zooming, the zoom lens having an F-number which is constant over an entire zoom range; and
 the zoom lens comprising a first variable stop and a second variable stop, the first variable stop being disposed in an object side of the third lens unit and having an aperture diameter changing for zooming, the second variable stop being disposed in an image side of the first variable stop and having an aperture diameter changing for zooming, 
 wherein the following conditional expressions are satisfied:
   0.90< Sw 1/ Tkw< 1.50, and 
   0.60< Sw 2/ Tkw< 1.00, 
 
 where Sw1 represents a distance from the first variable stop to an image plane at a wide-angle end, Sw2 represents a distance from the second variable stop to the image plane at the wide-angle end, and Tkw represents a distance from an exit pupil position to the image plane at the wide-angle end. 
 
     
     
       9. A zoom lens comprising, in order from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a fifth lens unit having a positive refractive power, the lens units being configured to change intervals between the respective neighboring lens units for zooming, the zoom lens having an F-number which is constant over an entire zoom range,
 the zoom lens comprising a first variable stop and a second variable stop, the first variable stop being disposed in an object side of the third lens unit and having an aperture diameter changing for zooming, the second variable stop being disposed in an image side of the first variable stop and having an aperture diameter changing for zooming, 
 wherein the following conditional expressions are satisfied:
   0.90< Sw 1/ Tkw< 1.50, and 
   0.60< Sw 2/ Tkw< 1.00, 
 
 
       where Sw1 represents a distance from the first variable stop to an image plane at a wide-angle end, Sw2 represents a distance from the second variable stop to the image plane at the wide-angle end, and Tkw represents a distance from an exit pupil position to the image plane at the wide-angle end. 
     
     
       10. An image pickup apparatus, comprising:
 a zoom lens comprising, in order from an object side to an image side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power, the lens units being configured to change intervals between the respective neighboring lens units for zooming, the zoom lens having an F-number which is constant over an entire zoom range,
 the zoom lens comprising a first variable stop and a second variable stop, the first variable stop being disposed between the first lens unit and the second lens unit and having an aperture diameter changing for zooming, the second variable stop being disposed in an image side of the first variable stop and having an aperture diameter changing for zooming, and 
 wherein the following conditional expressions are satisfied:
   0.90< Sw 1/ Tkw< 1.50, and 
   0.60< Sw 2/ Tkw< 1.00, 
 
 where Sw1 represents a distance from the first variable stop to an image plane at a wide-angle end, Sw2 represents a distance from the second variable stop to the image plane at the wide-angle end, and Tkw represents a distance from an exit pupil position to the image plane at the wide-angle end; and 
 
 a photoelectric transducer for receiving an image formed by the zoom lens. 
 
     
     
       11. An image pickup apparatus, comprising:
 a zoom lens comprising, in order from the object side to the image side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, a fourth lens unit having a positive refractive power, a fifth lens unit having a negative refractive power, and a sixth lens unit having a positive refractive power, the lens units being configured to change intervals between the respective neighboring lens units for zooming, the zoom lens having an F-number which is constant over an entire zoom range,
 the zoom lens comprising a first variable stop and a second variable stop, the first variable stop being disposed in an object side of the third lens unit and having an aperture diameter changing for zooming, the second variable stop being disposed in an image side of the first variable stop and having an aperture diameter changing for zooming, 
 wherein the following conditional expressions are satisfied:
   0.90< Sw 1/ Tkw< 1.50, and 
   0.60< Sw 2/ Tkw< 1.00, 
 
 where Sw1 represents a distance from the first variable stop to an image plane at a wide-angle end, Sw2 represents a distance from the second variable stop to the image plane at the wide-angle end, and Tkw represents a distance from an exit pupil position to the image plane at the wide-angle end; and 
 
 a photoelectric transducer for receiving an image formed by the zoom lens. 
 
     
     
       12. An image pickup apparatus, comprising:
 a zoom lens comprising, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a fifth lens unit having a positive refractive power, the lens units being configured to change intervals between the respective neighboring lens units for zooming, the zoom lens having an F-number which is constant over an entire zoom range,
 the zoom lens comprising a first variable stop and a second variable stop, the first variable stop being disposed in an object side of the third lens unit and having an aperture diameter changing for zooming, the second variable stop being disposed in an image side of the first variable stop and having an aperture diameter changing for zooming, 
 wherein the following conditional expressions are satisfied:
   0.90< Sw 1/ Tkw< 1.50, and 
   0.60< Sw 2/ Tkw< 1.00, 
 
 where Sw1 represents a distance from the first variable stop to an image plane at a wide-angle end, Sw2 represents a distance from the second variable stop to the image plane at the wide-angle end, and Tkw represents a distance from an exit pupil position to the image plane at the wide-angle end; and 
 
 a photoelectric transducer for receiving an image formed by the zoom lens.